A long-recognized challenge in manufacturing metallic parts is how to form high-precision/high aspect ratio (i.e., an article having a high ratio of length to thickness) structural and mechanical parts in an economical manner. The reason these types of articles are particularly difficult to manufacture is that, because they are intended for use as a mechanical or structural component, they need adequate strength, stiffness, and toughness to perform. But because they have a high aspect ratio, that is, their thickness is small in comparison to their length, the demands placed on the material performance and fabrication capability are very high.
Although there are many industries for which high-aspect ratio structural parts are required, one obvious example is the consumer electronic (CE) industry. CE manufacturers must produce products such as cellular phones, laptop computers, digital cameras, PDA's, televisions, that are generally comprised of integrated circuits, displays, and digital storage media, and which are packaged in a casing that often includes frame assemblies, and complex functional components such as hinges, slider bars, or other hardware with both mechanical and structural functions, as shown for example in FIG. 1. In addition, the consumer-driven demand for increasingly smaller CE products places a demand for increasingly thinner structural components (e.g. casings and frames) with increasingly larger aspects ratios and better mechanical performance.
Today, such casings, frames, and structural components are fabricated primarily from metal alloys or plastics. Plastics parts are generally very inexpensive owing to low raw material cost and cost efficient manufacturing processes. From a manufacturing perspective, plastics are easy to form into complex three dimensional net shapes with high precision and tolerance, excellent surface finish, and desirable cosmetic appearance. There are a number of excellent high-volume production techniques, such as, for example, injection molding, blow molding, and other thermoplastic forming methods that are highly efficient and cost effective at the typical temperatures (100-400° C.) and pressures (10-100 MPa) required for processing plastics. The low manufacturing cost of plastic hardware is driven partly by the low cost-processing requirements of net-shaped plastic parts. But, a significant fraction of the manufacturing cost savings in plastics processing arises from the very high mold-tool life. The exceptionally low processing pressures and temperatures give rise to remarkably high tool life, typically in the millions of cycles, thereby significantly reducing the mold-tool overhead cost per part. On the other hand, plastics have limited stiffness (elastic modulus), relatively low strength and hardness, and have limited toughness and damage tolerance. As a result, plastic parts are often a poor choice when mechanical performance is of importance as in many structural applications. For example, casing and frames made of plastics are highly susceptible to fracture on bending or impact, scratch and wear, and provide only limited rigidity and stability as a structural framework.
In contrast, metals and metal alloys have much higher stiffness and rigidity, strength, hardness, toughness, impact resistance, and damage tolerance which make them a superior choice for structural applications for precision parts with high aspect ratio. However, precision net-shape metal hardware is typically made either by casting, die forming/forging, or machining. For example, die casting with permanent (multiple use) mold took is often used to fabricate high volume low cost metal hardware, but is restricted to relatively low melting point alloys (melting temperatures less than 700° C.) such as aluminum, magnesium, zinc, etc. This is because typical tool-steel molds are often tempered at temperatures below 700° C., and processing above the tempering temperature will rapidly deteriorate the mold. Typical tool life in die casting of low-melting point metal alloys are on the order of hundreds of millions of cycles, that is, roughly one order of magnitude lower than in plastics processing. For more refractory, higher stiffness/strength alloys having higher melting temperatures such as steel and titanium alloys, the die casting melt temperatures (often >1500 C) far exceed the typical working temperature of steel tooling. Moreover, the die casting pressures required to cast net shapes are generally high (tens or hundreds of MPa). Consequently, tool life becomes a major cost limiting issue. Moreover, in die casting of metal alloys, the melt viscosities are very low (typically in the range of 10−5 to 10−3 Pa-s), and thus the melt flow is characterized by high flow inertia and limited flow stability. Consequently, the mold tool is rapidly filled by molten metal moving at high velocities (typically >1 m/s) and the metal is often atomized and sprayed into the mold creating flow lines, cosmetic defects, and a final part of limited quality and integrity. Accordingly, die casting is not commercially viable for titanium alloys, steels, or other refractory metal alloys.
As a result, when precision, complex net-shaped, high quality, high aspect ratio refractory metal hardware is required for structural applications in consumer electronic frames, casings, and structural parts, most manufacturers resort to machining the components. While machining steel and titanium alloys, for example, can meet the functional, cosmetic, and performance requirements for these high-aspect ratio electronic casings and frames, it is time intensive, inefficient, leads to large material waste, and results in very costly hardware. Accordingly, there is a growing need in the consumer electronics industry to produce high precision structural hardware with a material that matches or bests the stiffness, strength, toughness, hardness, and overall mechanical performance of refractory metals using an efficient cost effective process technology competitive with that currently used to manufacture plastic hardware.